A new experimental methodology has been developed for the definitive determination of articular cartilage on cartilage interfacial shear friction which occurs during accurately known and controlled mechanical conditions in vitro. The objective of the proposed research will be to apply this recently developed experimental technique to a detailed analysis of the mechanical interaction of geometrically well defined excised bovine and human articular cartilage interfaces. New electromechanical instrumentation, known as the Biorheometer, will be utilized along with computerized sampling, digitization and storage of the data. The responses will be documented for five experimental test categories: 1) the responses to statically applied loads on the sliding cartilge interfaces, 2) dynamic loading responses, 3) asymptotic steady-state frictional responses, 4) kinematic velocity parameter variations, and 5) variations in cartilage fluid environmental conditions (temperature, pH, and normal saline versus synovail fluid). Systematic scanning electron microscope examinations will be conducted on each specimen immediately following mechanical testing. Alternative specimen preparation and surface observational techniques will also be employed. By statistically and quantitatively evaluating any resultant surface topographical changes which have been produced on the cartilage tested region versis the neighboring untested region, it will be possible to correlate in a rigorous way the link between these specific surface ultrastructural alterations and the direct mechanical and kinematic conditions which caused them.